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Isotopes to determine water sources

Friday, 01 January 2010

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During 2009 the Centre for Ecosystem Management awarded a grant to Dimity Boggs and Ray Froend to undertake an investigation into the use of stable isotopes of water to investigate the water-use requirements of groundwater dependent plant communities located in the south-west of WA. Isotope analysis allows for the determination of the dependence of ecosystems on groundwater and can be used to complement qualitative assessments of dependence. It allows us to distinguish how much water is derived from deep groundwater versus surface soil-water. The patterns of water relations for four wetland plant communities indicated that the plants investigated were all using groundwater to some extent during the monitoring period. There was variability in groundwater use between species with Melaleuca preissiana consistently using a high to exclusive proportion of groundwater. Shallow rooted shrubs accessed a combination of surface soil-water in late spring with increasing proportions of groundwater as the summer progressed. The success of the isotopic tracing method relies on a clear discrimination between the isotopic signatures of different waters sources which were surprisingly good for this investigation considering the very shallow water tables and high rainfall of the region. The analyses for this project were undertaken within ECU's School of Natural Sciences Isotope Facility which has recently purchased a Los Gatos Stable water Isotope Analyser through University and Faculty funds. The new equipment allows for rapid and simultaneous analysis of both isotopes in water at a fraction of the cost of the separate determination of hydrogen and oxygen isotopes on a mass spectrometer.